may be that even Risch hasn't even tried it. generally speaking the 'egg crates' are a poor imitation of Sonex and other competing products. While there is some attenuation of frequencies the effect is quite dependent upon the foam density. Understand, that these products are designed to pass air for their typical use is in mattresses, pillows, sofas, etc. The expense for many can be prohibitive for Sonex and once you've started cutting, well there goes any hope of returning them. There are other alternative that may be equally cost effective and not present such an effective way of ruining the appearance of a room. Insulation batting (R-19) stapled to the wall, paper side down, and then covered with cloth may make for something aesthetically pleasing. Also one could use acoustic panels which I believe are made by Owens Corning. Try contacting Owens Corning for I believe they, as well as others, have literature indicating the sound deadening properties of their products and that includes insulation.
Oh, one more thing! You'll find that untreated foam is quite a hazard should there ever be a fire. There are treated versions but you need to ask.